1. Field of the Invention
The present invention relates generally to a fluorescent-light image display method and apparatus therefor, and more particularly to a method of and apparatus for detecting the fluorescent-light emitted from a living-tissue subject upon irradiation thereof by a stimulating-light and displaying the detected fluorescent light as an image representing the data relating to the living-tissue subject.
2. Description of the Related Art
It has been known in the field of radiology that when a living-tissue subject is irradiated by a stimulating wavelength having a predetermined wavelength, the strength of the fluorescent light emitted from the normal tissue and the strength of the fluorescent light emitted from the diseased tissue differ. Technologies have been proposed, wherein, by making use of this difference, a living-tissue subject is irradiated by a stimulating-light of a predetermined wavelength and by receiving the fluorescent-light image emitted from the living-tissue subject, the location and range of infiltration of a diseased tissue is displayed as a fluorescent-light image.
Normally, upon irradiation by stimulating-light, as shown in FIG. 21, because a strong fluorescent-light is emitted from normal tissue and a weak fluorescent-light is emitted from diseased tissue, by measuring the strength of the fluorescent light, the state of the disease can be determined.
Basically, this type of fluorescent-light image display apparatus comprises a stimulating-light emitting means for projecting the stimulating-light onto a living-tissue subject, a fluorescent-light image obtaining means for obtaining a fluorescent-light image of the fluorescent light emitted from the living-tissue subject, and a display means for receiving the output of the fluorescent-light image obtaining means and displaying aforementioned fluorescent-light image. In many cases, this apparatus is incorporated into an endoscope for insertion into a body cavity of a patient, a colposcope, or a surgical-use microscope.
However, when using a fluorescent-light image display apparatuses such as that described above, because there is unevenness on a the surface of a portion of the living-tissue subject, the distance between the stimulating-light emitting system and the living-tissue subject is not uniform, and the intensity of the stimulating-light irradiating a living-tissue subject is generally not uniform at all positions of the living-tissue subject. The strength of the fluorescent light emitted from the living-tissue subject is substantially proportionate to the degree of the stimulating-light irradiation received by the living-tissue subject, and the degree of stimulating-light irradiation received by the living-tissue subject is in inverse proportion to the square of the distance. Therefore, there are cases in which a diseased tissue located closer to the stimulating-light emitting system emits a stronger fluorescent light than a normal tissue located at a position further removed from the stimulating-light emitting system, and if an operator makes a determination as to the state of the disease based solely on the strength of the fluorescent light, an erroneous diagnosis result is obtained.
In order to reduce the uncertainty and itinerant precariousness in diagnosis due to the circumstances described above, the applicants of the present application propose a fluorescent-light image display apparatus for displaying a pseudo color image, wherein a narrow-band fluorescent-light image near the 480 nm wavelength range is obtained of the normal tissue, and a wide-band fluorescent-light image of the fluorescent light in the visible spectrum is obtained of the diseased tissue, a division value is obtained of the light strength of the wide-band image fluorescent-light image, and based on this division value, aforementioned pseudo color image is displayed.
That is to say, the term representing the strength of the fluorescent light, which is dependent on the distance between the stimulating-light source and the living-tissue subject, is cancelled by aforementioned division process, and an image displaying only the difference in the spectra of the fluorescent light is obtained.
Further, on the other hand, the applicants of the present application propose a method of facilitating discernment of the state of a living-tissue subject by obtaining the ratio of the strength of the stimulating-light received by the irradiated living-tissue subject and the fluorescent light emitted therefrom, that is, the value reflecting the fluorescent light emission output, which is a value that is not affected by the distance or angle from which the stimulating-light has been projected onto the living-tissue subject.
When obtaining the value reflecting aforementioned fluorescent light emission output, because the stimulating-light is not absorbed the same by the various types of tissue, even if the distribution of the light strength of the irradiated stimulating-light is measured, the distribution of the light strength of the stimulating-light received by the living-tissue subject is not correctly measured.
Here, one strategy for obtaining the fluorescent light uptake rate is to irradiate a living-tissue subject with a near-infrared light, which is absorbed uniformly by various types of tissue, as a reference light and to photograph a reflected-light image of the reflected reference-light reflected from the living-tissue subject; the light strength of this reflected-light image is used in place of the light strength of the stimulating-light received by the living-tissue subject and a division value of the fluorescent-light image and the light strength of the reflected-light image is obtained, and based on this division value, a pseudo color image is displayed.
That is to say, by aforementioned division process, the term representing the light strength of the fluorescent-light, which is dependent on the distance between the stimulating-light source and the living-tissue subject is cancelled, and an image reflecting only the difference in the fluorescent light emission output is obtained.
However, as described above, by performing aforementioned division process between fluorescent-light images or between a fluorescent-light image and a reflected-light image, although the pseudo color image in which the distance data has been cancelled contains the data relating to the fluorescent light emitted from the living-tissue subject, after being used as a diagnostic tool for determining the state of a disease, it becomes a composite-image in which the valuable data relating to the form of the living-tissue subject has been omitted. And once again, to the operator, the composite-image gives the impression of flatness devoid of any unevenness whatsoever, and becomes considered as a dubious image.